Immiscible Exchange Flows in Near-Horizontal Rotating Pipes With Applications in Well Cementing

Primary and remedial cementing are critical in well construction to ensure zonal isolation and structural support. In horizontal or tilted wellbores, gravity-driven exchange flows, caused by density differences between drilling mud and cement slurry, can occur and result in stratified layers, weak spots, or voids, compromising cement quality. These challenges intensify during complex procedures such as rotating-while-cementing or operational pauses, where fluid redistribution occurs. Our study numerically examines immiscible exchange flows in near-horizontal pipes with axial rotation, modeling rotating-while-cementing conditions. A heavier displacing fluid occupies the upper pipe section, while a lighter fluid fills the lower section, creating a density-unstable configuration. Simulations assess the effects of rotational speed, density differences, and pipe inclination. Our results reveal predominantly counter-current stratified flows, with increased rotational speed amplifying interfacial instabilities and kinking waves but reducing displacing fluid frontal velocity. Conversely, greater density differences and inclinations away from horizontal affect exchange flows by increasing interfacial frontal velocities.